Triple DES
In cryptography, Triple DES (3DESGoogle search for "3DES") is the common name for the Triple Data Encryption Algorithm (TDEA) block cipher, which applies the Data Encryption Standard (DES) cipher algorithm three times to each data block. Because of the availability of increasing computational power, the key size of the original DES cipher was becoming subject to brute force attacks; Triple DES was designed to provide a relatively simple method of increasing the key size of DES to protect against such attacks, without designing a completely new block cipher algorithm. Definitive standards The Triple Data Encryption Algorithm (TDEA) is defined in each of: * ANSX9.52 is sometimes erroneously referred to as ANSI X9.52, however the standard itself has the designation ANS X9.52. X9.52-1998 Triple Data Encryption Algorithm Modes of Operation''X9.52 defines TDEA as a compound operation of the Data Encryption Algorithm specified in ANSI X3.92-1981 ''Data Encryption Algorithm, and does not include the DEA specification. Thus X9.52 must be read in conjunction with X3.92. (withdrawn) * [http://csrc.nist.gov/publications/fips/fips46-3/fips46-3.pdf FIPS PUB 46-3 Data Encryption Standard (DES)] (PDF) (withdrawnFederal Register vol 70, number 96, [http://csrc.nist.gov/publications/fips/05-9945-DES-Withdrawl.pdf Announcing Approval of the Withdrawal of Federal Information Processing Standard (FIPS) 46–3, Data Encryption Standard (DES); FIPS 74, Guidelines for Implementing and Using the NBS Data Encryption Standard; and FIPS 81, DES Modes of Operation] (PDF)) * * [http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=37972 ISO/IEC 18033-3:2005 Information technology — Security techniques — Encryption algorithms — Part 3: Block ciphers] Name of the algorithm The earliest standard that defines the algorithm (ANS X9.52, published in 1998) describes it as the "Triple Data Encryption Algorithm (TDEA)" — i.e. three operations of the Data Encryption Algorithm specified in ANSI X3.92 — and does not use the terms "Triple DES" or "DES" at all. FIPS PUB 46-3 (1999) defines the "Triple Data Encryption Algorithm (TDEA)", but also uses the terms "DES" and "Triple DES". It uses the terms "Data Encryption Algorithm" and "DES" interchangeably, including starting the specification with: and Triple Data Encryption Algorithm (TDEA, as described in ANSI X9.52).}} NIST SP 800-67 (2004, 2008NIST SP 800-67 version 1 was published in May 2004. It was revised in May 2008, as version 1.1, making a correction and clarification to the list of weak and semi-weak keys. Both versions use the same terminology.) primarily uses the term TDEA, but also refers to "Triple DES (TDEA)". ISO/IEC 18033-3 (2005) uses "TDEA", but mentions that: None of the standards that define the algorithm use the term "3DES". Algorithm Triple DES uses a "key bundle" which comprises three DES keys, K1, K2 and K3, each of 56 bits (excluding parity bits). The encryption algorithm is: :ciphertext = EK3(DK2(EK1(plaintext))) I.e., DES encrypt with K1, DES decrypt with K2, then DES encrypt with K3. Decryption is the reverse: :plaintext = DK1(EK2(DK3(ciphertext))) I.e., decrypt with K3, encrypt with K2, then decrypt with K1. Each triple encryption encrypts one block of 64 bits of data. In each case the middle operation is the reverse of the first and last. This improves the strength of the algorithm when using keying option 2, and provides backward compatibility with DES with keying option 3. Keying options The standards define three keying options: *Keying option 1: All three keys are independent. *Keying option 2: K1 and K2 are independent, and K3 = K1. *Keying option 3: All three keys are identical, i.e. K1 = K2 = K3. Keying option 1 is the strongest, with 3 x 56 = 168 independent key bits. Keying option 2 provides less security, with 2 x 56 = 112 key bits. This option is stronger than simply DES encrypting twice, e.g. with K1 and K2, because it protects against meet-in-the-middle attacks. Keying option 3 is equivalent to DES, with only 56 key bits. This option provides backward compatibility with DES, because the first and second DES operations cancel out. It is no longer recommended by the National Institute of Standards and Technology (NIST),NIST SP 800-67 and is not supported by ISO/IEC 18033-3. Other terms used to refer to the keying options "Keying option n''" is the term used by the standards (X9.52, FIPS PUB 46-3, SP 800-67, ISO/IEC 18033-3) that define the TDEA. However, other terms are used in other standards and related recommendations, and general usage. *For keying option 1: **3TDEA, in NIST SP 800-57[http://csrc.nist.gov/publications/nistpubs/800-57/sp800-57-Part1-revised2_Mar08-2007.pdf NIST Special Publication 800-57 ''Recommendation for Key Management — Part 1: General (Revised), March, 2007] (PDF) and SP 800-78-2[http://csrc.nist.gov/publications/nistpubs/800-78-2/sp800-78-2.pdf NIST Special Publication 800-78-2, Cryptographic Algorithms and Key Sizes for Personal Identity Verification, February 2010] (PDF) **Triple-length keys, in general usage *For keying option 2: **2TDEA, in NIST SP 800-57 and SP 800-78-1 **Double-length keys, in general usage Encryption of more than one block As with all block ciphers, encryption and decryption of multiple blocks of data may be performed using a variety of modes of operation, which can generally be defined independently of the block cipher algorithm. However ANS X9.52 specifies directly, and NIST SP 800-67 specifies (via SP 800-38A[http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf NIST Special Publication 800-38A, Recommendation for Block Cipher Modes of Operation, Methods and Techniques, 2001 Edition] (PDF)), that some modes shall only be used with certain constraints on them that do not necessarily apply to general specifications of those modes. For example, ANS X9.52 specifies that for cipher block chaining, the initialization vector shall be different each time, whereas ISO/IEC 10116[http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=38761 ISO/IEC 10116:2006 Information technology — Security techniques — Modes of operation for an n-bit block cipher] does not. FIPS PUB 46-3 and ISO/IEC 18033-3 define only the single block algorithm, and do not place any restrictions on the modes of operation for multiple blocks. Security In general Triple DES with three independent keys (keying option 1) has a key length of 168 bits (three 56-bit DES keys), but due to the meet-in-the-middle attack the effective security it provides is only 112 bits. Keying option 2 reduces the key size to 112 bits. However, this option is susceptible to certain chosen-plaintext or known-plaintext attacksRalph Merkle, Martin Hellman: [http://www.cs.purdue.edu/homes/ninghui/courses/Spring04/homeworks/p465-merkle.pdf On the Security of Multiple Encryption] (PDF), Communications of the ACM, Vol 24, No 7, pp 465–467, July 1981.Paul van Oorschot, Michael J. Wiener, [http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.66.6575&rep=rep1&type=pdf A known-plaintext attack on two-key triple encryption] (PDF), EUROCRYPT'90, LNCS 473, 1990, pp 318–325. and thus it is designated by NIST to have only 80 bits of security.[http://csrc.nist.gov/publications/nistpubs/800-57/sp800-57-Part1-revised2_Mar08-2007.pdf NIST Special Publication 800-57 Recommendation for Key Management — Part 1: General (Revised), March, 2007] (PDF) The best attack known on keying option 1 requires around 232 known plaintexts, 2113 steps, 290 single DES encryptions, and 288 memoryStefan Lucks: [http://th.informatik.uni-mannheim.de/People/Lucks/papers/pdf/3des.pdf.gz Attacking Triple Encryption] (PDF), Fast Software Encryption 1998, pp 239–253. (the paper presents other tradeoffs between time and memory). This is not currently practical and NIST considers keying option 1 to be appropriate through 2030. If the attacker seeks to discover any one of many cryptographic keys, there is a memory-efficient attack which will discover one of 228 keys, given a handful of chosen plaintexts per key and around 284 encryption operations.Eli Biham: [http://www.cs.technion.ac.il/users/wwwb/cgi-bin/tr-get.cgi/1996/CS/CS0884.ps.gz How to Forge DES-Encrypted Messages in 228 Steps] (PostScript), 1996. Usage The electronic payment industry uses Triple DES and continues to develop and promulgate standards based upon it (e.g. EMV).[http://www.emvco.com/specifications.aspx?id=155 EMV 4.2 Specifications, Book 2 - Security and Key Management, version 4.2, June 2008]VISA Microsoft OneNote and Microsoft Outlook 2007 use Triple DES to password protect user content.Daniel Escapa's OneNote Blog - Encryption for Password Protected Sections, November 2006Microsoft - Encrypt E-mail Messages, Outlook 2007 See also * Data Encryption Standard (DES) * DES-X * Advanced Encryption Standard (AES) * Horst Feistel * Walter Tuchman References and notes Category:Broken block ciphers Category:Data Encryption Standard bg:Triple DES ca:Triple DES cs:TripleDES da:Triple DES de:Data Encryption Standard#Triple-DES es:Triple DES eu:DES Hirukoitza fr:Triple DES id:Triple DES it:Triple DES he:3DES nl:3DES-encryptiealgoritme ja:トリプルDES no:Trippel DES pl:3DES pt:3DES ro:3DES ru:Triple DES simple:Triple DES fi:3DES sv:3DES uk:Triple DES zh:3DES